Composite caustic silica gel manufacturing method and gels made thereby

ABSTRACT

New silica gel materials and novel methods of producing such are provided. The method itself entails a manner of mixing the reactants together in a one-pot process such that the time required for aging is reduced without compromising the ability to target pore size production. In such a way, the pH of the reaction drives pore size development, thereby permitting a more efficient process to be followed in terms of expensive drying/heating steps being reduced timewise, if not altogether. Furthermore, in one embodiment, the resultant gel materials exhibit a certain pore size minimum while simultaneously exhibiting a degree of softness heretofore unavailable. As such, not only is this novel method more efficient in silica gel manufacture, but the resultant materials are completely novel as well. The gel materials made therefrom may be utilized in a variety of different end uses, such as cooking oil filtration, soft skin cleansers, dental abrasives, and the like. Methods of production and use, as well as the novel gel materials themselves, particularly caustic and composite gels, are thus encompassed within this invention.

FIELD OF THE INVENTION

The present invention relates generally to new silica gel materials andnovel methods of producing such. The method itself entails a manner ofmixing the reactants together in a one-pot process such that the timerequired for aging is reduced without compromising the ability to targetpore size production. In such a way, the pH of the reaction drives poresize development, thereby permitting a more efficient process to befollowed in terms of expensive washing/filtering steps being reducedtimewise, if not altogether. Furthermore, in one embodiment, theresultant gel materials exhibit a certain pore size minimum whilesimultaneously exhibiting a degree of softness heretofore unavailable.As such, not only is this novel method more efficient in silica gelmanufacture, but the resultant materials are novel as well. The gelmaterials made therefrom may be utilized in a variety of different enduses, such as cooking oil filtration, soft skin cleansers, dentalabrasives, and the like. Methods of production and use, as well as thenovel gel materials themselves, particularly caustic and composite gels,are thus encompassed within this invention.

BACKGROUND OF THE INVENTION

Silica gels have been manufactured for many years and utilized in aplethora of different applications, ranging from abrasives to desiccantsto thickeners and the like. The typical manufacturing process followedfor silica gel production involves careful feeding of an acid and waterglass solution through a narrow tube into a large cylindrical vessel.The gel will form nearly instantaneously so it is imperative that thefeed be undertaken in such a fashion as to permit the resultant highlyviscous gel product to form from the bottom of the cylinder and fill upthe entire structure without clogging the feed system itself. Uponcomplete gel formation, the cylinder is then tipped downward and apiston is triggered to force the gel (in a large cylindrically shapedsemi-solid form) out of the cylinder and through a series of meshscreens of differing gauge in order to “slice” the large gel mass intodiscrete cubic (or chunks) shapes. The resultant small gel cubes arethen ammoniated and subjected to heating for a sufficient time toprovide a desired pore size level and reinforcement simultaneously. Thedried particles can then be milled to a desired size.

Classic silica gel manufacturing methods, involving the same generalinstantaneous gel production as discussed above, are disclosed withinU.S. Pat. Nos. 3,794,712 and 3,819,811, to Aboutboul et al., as well asU.S. Pat. No. 4,148,864 to Groth et al. In more detail, hydrous silicagels are the result of the classical reaction of an alkali silicate witha mineral acid. Sulfuric acid is the most commonly used acid, althoughother mineral acids such as hydrochloric acid, nitric acid or phosphoricacid can be used. Sodium or potassium silicate may be used as the alkalisilicate, with sodium silicate being preferred. The acid is added to thealkali silicate solution until a pH of less than about 5 is reached,with a pH of about 3 to 4.5 being most common. The alkali silicatesolution can be mixed during this addition. The resulting product is asolid silica which includes the liquid phase. That is, the silica fullyincludes the water within its pores. For this reason that the solidphase contains the liquid phase, these silica materials have been termedsilica hydrogels, with the dried silica being termed a silica gel. Themode of drying will determine whether the silica gel is a silica aerogelor a silica xerogel. Such silica hydrogels after synthesis have a watercontent of about 50 to 85 percent by weight.

Traditionally, in producing these silica hydrogels, the alkali silicatesolution has an SiO₂ concentration of about 6 to 30 percent by weight. Astoichiometric excess of acid is used, thereby reaching the lowpreferred pH of 3 to 4.5. After the silica hydrogel is formed, it iswashed with ammonia to remove excess salts and then dried (by anystandard manner, such as oven drying, spray drying, flash drying, andthe like) for a specified period of time to target pore sizes and porevolumes therein.

Due to the instantaneous gel formation effectuated within typical gelmanufacturing equipment, there is no possibility for the introduction ofextra caustic agent within the typical gel reaction process. If such anaddition were made, the mineral acid reactant would be neutralized andno appreciable gel formation would occur. Conventionally, subsequent tothe gel formation, the cylindrical mass is sliced into individual gelunits; so gel unit would be modified to an appreciable degree uponexposure to a caustic material either. Thus, there has been no teachingof modification during gel formation steps previously.

As with other silica products, the generation of a specific pore sizeand particle size is the frequent goal of silica gel materialsmanufacture. Gels can be targeted for any such physical characteristicdepending on the manufacturing method employed, in particular, as itpertains to the aforementioned traditional gel manufacturing method, thelonger the aging time at a certain temperature will cause a certainlevel of pore size and pore volume to result. In general, the followingof this aforementioned typical gel manufacturing procedure entails alarge amount of heat over a long period of time in order to target thedesired pore size. As such, the methods followed over the years haveproven to be rather inefficient and costly. Likewise, the machinery andinstrumentation required for such gel manufacture are, as thedescription above indicates, rather complex in nature and bulky, not tomention potentially prone to mechanical difficulties. Hence, a lesscomplex method of manufacture with typical silica production apparatuseswould be a preferable development for the silica gel manufacturer aswell. Furthermore, since caustic additions have heretofore beennonexistent for gel formation methods, the introduction of any causticmaterials that could impart a metal species to the gel surface to form acomposite gel has not been disclosed within the prior art either. Amethod that enhances such composite formation (such as with desirablealkaline earth metal species) would thus be desired within the silicagel industry. Yet, to date, no such efficient and reliable process hasbeen forthcoming.

BRIEF DESCRIPTION OF THE INVENTION

It is therefore one advantage of this novel process to produce a silicagel material through a process that does not require a first step offorming a semi-solid gel of low solids content, but actually entails afirst step of producing gel materials in liquid phase form. Anotheradvantage of this novel process is that the aging times required toprovide a proper solid material is much shorter than that for thetypical silica gel production method as well as the ability to avoidintroduction of ammoniacal solvents. Yet another advantage of this novelprocess is the ultimate silica gel material exhibits the similar poresizes as previously required of long aging times through pHmodifications instead. An additional advantage with the presentinvention is the relative ease in salt removal provided with loweramounts of needed water for such a process step, thus providing a muchmore efficient method due to lower washing and filtration and shorteraging times than for traditional silica gel production procedures. Stillanother advantage is that this process provides a novel soft gelmaterial with large pore sizes upon incorporation of proper high pHcaustic during the manufacturing thereof. Yet another advantage is theease of producing (in like efficient fashion) reliable composite gelsfrom base components reacted with the resultant gels during gelproduction.

Accordingly, this invention encompasses a method of producing a silicagel material comprising the sequential process steps of a) initiallyproducing a silicic acid sol through alkali metal silicate addition to amineral acid, wherein the reaction occurs at a target pH level ofbetween 1.5 and 4.0; b) quenching said silicic acid sol in a hot watermedium to solidify said sol into a polysilicic acid gel; c) aging theresultant gel of step “b” in salt water; d) washing said aged gel ofstep “c” to remove excess salt; and e) drying said washed gel of step“d” to form a dry silica gel.

Also encompassed within this invention is a silica gel materialexhibiting a Perspex abrasion value of at most 3 at an average particlesize of at most 42 Å and further exhibiting a mean pore size of at least20 Å. A filter medium and/or cleansing composition comprising such anovel silica gel material is encompassed as well. Furthermore, causticgels of pH greater than 7.0 as well as composite silica gels of alkalineearth metal are encompassed within this invention as well.

DETAILED DESCRIPTION OF THE INVENTION

The term “Sol” is intended to encompass any suspension of fine silicaparticles in an aqueous media. The term “gel” is intended to encompass athree-dimensional network formed by silica particles, in either wet ordry form. The term “composite gel” is intended to encompass silica gelthat includes with additional species present at least on the surfacethereof in addition to the reaction product of sodium silicate andsulfuric acid.

The term “hot water medium” is intended to encompass an aqueous solventpresent at a temperature of from about 65 to about 100° C.

All U.S. patents mentioned herein are hereby entirely incorporated byreference.

It has thus been determined, surprisingly, that acidic or caustic silicagel materials (otherwise known as polysilicic acid gel), as well asalkaline earth metal silica gel composites, may be produced in atypicalsilica gel manufacturing apparatuses, such as, as one example, withinapparatuses primarily utilized for precipitated silica materialproduction, through a process that entails the following sequentialsteps (for silica gels alone):

(1) making polysilicic acid in the reactor, (2) solidifying thepolysilicic acid solution into gel form, using temperature and pHcontrol in the subsequent tank, (3) aging the gel in salt water, (4)washing the gel with a press filter to remove excess and free salt, and(5) drying the pressed cake, by oven or flash dryer. In this processfilter feed tank could be used for step (2) and (3). The resulting gelfrom this process usually remains acidic (pH<=6.5) and such a resultantgel exhibits excellent properties for certain filter media applications,among other end uses. Additionally, though a pH adjustment can beperformed in step (2), to create a higher pH gel through causticintroduction during step (2), by subsequently controlling the pH of thefinal pH in step (3), a caustic gel (pH>7) with larger pore volumecapacity and larger pore diameter can be produced as a result. If analkali metal hydroxide is utilized as the caustic material (such assodium hydroxide), the high solubility of the sodium species within thereaction medium creates a caustic environment in which the sodium cationwashes from the gel during such a step. However, if an alkaline earthmetal compound is utilized as the caustic additive (such as calciumhydroxide, i.e., slaked lime, or magnesium hydroxide), the lowsolubility properties of the metal species results in the ability ofsuch metals to aggregate on the gel surface within the high pHenvironment, thus creating a metal/gel composite. As noted above, theintroduction of a high pH caustic enables pore size, pore diameter,etc., modifications within the produced gel in order to avoid agingsteps of long duration with high temperatures, thereby permitting a muchquicker and more efficient manner of tuning the ultimate gel materials'physical properties; the ability to impart other properties in terms ofcaustic and/or composite structures is an unexpected added benefit ofsuch an efficient gel production method. Thus, the pore volume anddiameter are surprisingly tunable with differing levels of added causticintroduced within this second step, contrary to the past possibilitiesavailable from typical and traditional gel production processes. Incomparison with acidic gel wet cakes, improved washing efficiency of thecaustic gel wet cake is observed. Through the utilization of a vacuumfilter and the same amount of water, caustic wet gel cakes can be washedwith less than half of the time as compared to the acidic wet gel cake,and exhibits a lower final salt content. The basic silica gel should bebeneficial as neutralizing high capacity absorbents for (acidic)contaminants encountered. For example, such gels are highly effective atabsorbing undesirable components from acidic flue gases, such as sulfuroxides (SOx) and nitrogen oxides (NOx), as well as free fatty acids fromused cooking oil formulations (as well as myriad other uses, such as, asone non-limiting possibility, purification during beer processing). Thecaustic utilized for the high pH gel synthesis methods herein includenon-limiting examples such as sodium hydroxide and sodium silicate (dueto availability and cost), although any reactant that provides asufficiently high pH level (greater than 7.0, for instance) within thegel reaction may be utilized as well.

As for such composite silica gel materials, initially it is important tonote that a silica co-gelled with metal hydroxide shows increased porevolume and pore diameter than those without such species presentthereon. Calcium and/or magnesium composite gels have the potential inextra binding capabilities for different chemicals as compared to sodiumhydroxide caustic gel as well. The said product is silicic acid gel(made through the same basic method noted above) co-gelled with slakedlime slurry and/or magnesium hydroxide slurry. After washing and flashdrying, the resulting gel has higher pore volume (capacity) than thestandard silica gels (and even more so than sodium caustic gel, whichhas better properties than standard silica gels as well), even with lessamount of caustics added. The process of co-gelling is achieved bydigesting slaked lime or magnesium slurry in a drop tank at hightemperature first, then introducing the previously made liquidpolysilicic acid solution therein (dropwise, preferably). In this way,the calcium hydroxide and/or magnesium hydroxide are intermingled and/orinteract with the acidic silica solution and form a composite gel due tothe low solubility levels (as noted above) of the calcium and magnesiumions. The hydroxide slurries in this invention serve as pore structureimprovement additives in the process and as binding capabilitiesenhancer in the final products to various possible contaminants.Possible applications of these gels include SO₂ absorption in the fluegas from coal-fired power plants, among other acidic contaminants (NOx),as well as mercury removal from such flue gas streams. Such asilica-based product will also exhibit ability for reuse in variousother applications subsequent to flue gas purification (as opposed tothe inability of activated carbon to be usable for any furtherpurposes).

As noted above, traditional gel synthesis has always been considered atedious process which required special equipment for washing anddewatering as well as moving the hydrated gel. It is not uncommon for atypical gel synthesis to require washing/aging times of 4 to 24 Hrs toachieve the target salt levels. Theory dictates that gel washing isachieved by a diffusion process whereby water slowly migrates into thepore structure of the gel from outside-in, and in the process displacessalt outwards. Such a process is time consuming and costly. To combatthis problem gel manufacturers typically achieve more effective washingby decreasing the gel agglomerated size thereby decreasing the masstransfer zone, or increasing the wash water temperature since thesesalts are in most cases more soluble at higher temperature, or possiblysubstituting the alkali metal silicate raw material with salt freeorganic silanes.

The present invention thus relates to a process of synthesizing a silicagel/silicic acid gel (either acidic or caustic in nature, as well aspotentially a composite gel) of either predominantly micro or mesoporousproperties which dewaters and washes at a pace unmatched by conventionalgel synthesis thereby permitting a more efficient silica gel productionmethod. Although the preferred embodiments described herein involve theutilization of typical precipitated silica production equipment, inactuality, any type of production scheme can be followed, including anytype of manufacturing equipment, as long as certain process steps areincluded.

Such an inventive method was not a simple modification from typical gelsynthesis procedures as there were significant technical hurdles toimplementation and success for such a drastically modified process. Forexample, dewatering the gel may be a standard process step; however, todo so without deleteriously affecting the performance capabilities ofthe end product, particularly as a filter medium, was problematic.Furthermore, the amount of water necessarily required in order tothoroughly wash gel products in order to remove highly undesirable saltresidues is generally very high. In order to provide an acceptablealternative gel production method, it would be required to utilize loweramounts of wash water, if possible. Additionally, and potentially mostimportantly, the ability to reduce such wash water amounts wouldinevitably require the production of small agglomerates of gel material.The problem in such an instance would be the ability to simultaneouslyprovide such easily washed large amounts of small agglomerates whilepreventing the clumping of such agglomerates during dewatering andwashing into non-pumpable masses of gel.

The preferred manufacturing equipment for this inventive method wastypical silica precipitation equipment that was not significantlymodified to any extent. As noted above, surprisingly, it was found thatsuch atypical gel manufacturing equipment was possible for theproduction of a silica gel in a more efficient manner than traditionalsilica gel production processes, while also allowing for a tunable porediameter product through pH control rather than through aging timedifferences, all without compromising the provision of a silica gelmaterial that still exhibits sufficiently high gel-typical high surfacearea characteristics.

Such a manufacturing capability was permitted through the followingmethod steps:

-   1. Making a silicic acid sol by Alkali metal silicate addition to a    mineral acid to a target pH values of between 1.5 and 4.0 to form a    quasi-stable sol. (pH control in this stage is critical as it is    this reaction pH that dictates the pore size distribution in the    final product)-   2. Quenching the sol in a hot water medium to solidify the silicic    acid sol into the more stable polysilicic acid gel by using    temperature and pH control in the subsequent tank.

The hot water medium essentially provides the multiple functions of

-   -   i. Speeding up the gel process as a result of the increased        temperature,    -   ii. Diluting the salt present in the sol thereby requiring less        washing less washing,    -   iii. Having the gel form into discrete individual agglomerates        which allowed for the migration of salt across a shorter        distance thereby speeding up wash time;

-   3. Optionally introducing a caustic in the form of an alkali metal    hydroxide or alkaline earth metal hydroxide,

-   4. Aging the gel in salt water,

-   5. Washing the gel with press filter to rid the excess salt,

-   6. Drying the pressed cake, and

-   7. Optionally milling the dried gel.

Such a process avoids silica gelation in the reactor, instead gellingthe silica in the filter feed tank, thus enabling the gel to be madeusing common precipitation reactors. The transfer of the polysilicicacid solution into the filter feed tank can be varied, either throughthe utilization of pumps or reliance on gravity.

The inventive silica gels herein described may be produced within anytype of silica manufacturing equipment as long as the aforementionednecessary process steps are followed. Typically, the inventive silicagel is prepared by mixing an aqueous alkali metal silicate solution,usually sodium silicate, and an aqueous mineral acid solution, usuallysulfuric acid, to form a silica hydrosol and allowing the hydrosol toset to a hydrogel. The concentration of the acid solution is generallyfrom about 5 to about 70 percent by weight and the aqueous silicatesolution commonly has an SiO₂ content of about 6 to about 25 weightpercent and a weight ratio of SiO₂ to Na₂O of from about 1:1 to about3.4:1. The reaction is generally carried out at temperatures of fromabout 15 to about 80° C. and typically is carried out at an ambienttemperature (i.e., from about 20 to 25° C. at about 1 atmospherepressure).

The relative proportions and concentrations of the reactants areselected so that the hydrosol contains from about 5 to about 20 weightpercent SiO₂ and has a pH of from about 1 to about 11. When the quantityof acid reacted with the silicate is such that the final pH of thereaction mixture is acidic, typically from about 1 to 5, the resultingproduct is considered an acid-set hydrogel. The hydrogel granules arethen washed with water or acidified water to remove residual alkalimetal salts which are formed in the reaction. Acidified water ispreferred and usually has a pH of from about 1.0 to about 5.0,preferably from about 2.5 to about 4.5. The acid may be a mineral acidsuch as sulfuric acid, hydrochloric acid, nitric acid, or phosphoricacid or a weaker acid such as formic acid, acetic acid, oxalic acid,citric acid, tartric acid, nitriloacetic acid, ethylenediamine-tetraacetic acid, or propionic acid. The water usually has atemperature of from about 80 to about 200° F. (27-93° C.), preferablyabout 90° C.). Generally, the hydrogel is washed for a period of fromabout 0.5 to about 8 hours.

The resulting gel in the filter feed tank is aged for a time of from 0.5to 4 hours, at a temperature of from 65 to 100° C., and, depending onthe resultant silica gel desired, at a pH level of either acidic (lessthan 6.5) or basic (above 7.0). After aging, the resultant gel is thenreslurried and filtered via a press filter for washing and filtering.The pressed cake can be dried by any conventional means such as ovendrying, tray drying, flash drying, or spray drying and ground in a fluidenergy mill, hammer mill, or other known mill to the desired particlesize. Generally, the ground gels have a weight median particle diameterof from about 1 to about 40 microns.

The resultant gels can be collected prior to washing and filtering andthen introduced, as a polysilicic acid gel liquid, into a sample ofcalcium hydroxide, lime, magnesium hydroxide, and the like, to permitreaction to form a composite gel. The reaction may be at a temperatureof from 65 to 100° C., for a time of from 0.5 to 4 hrs. Subsequently,the resultant product is washed for excess salt, as above, dried, asabove, collected and possibly milled as well, to provide a finishedcomposite gel material in powder, granulate, or other like form.Subsequently, the resultant product is washed for excess salt, as above,dried, as above, collected and possibly milled as well, to provide afinished composite gel material in powder, granulate, or other likeform.

Silica gels made by this process typically will have BET surface areasof 350-1000 m₂/g with pore diameter of 17 Å-45 Å. In experiments wherethe reaction pH is maintained at below 1.75 before the quenching stagethe pores were found to be predominantly if not completely micropore insize (<20 Å). In other experiments where the drop pH was maintainedbetween 3 and 4.0 the final product was predominantly mesoporous (20 Åand 45 Å). As for the caustic gels, as well as the composite gels, thepore sizes ranged from about 60 to 200 Å.

This silica hydrogel is used in a preferred average particle size rangeof about 2 to 30 microns. This average particle size range is an averageparticle size by weight, as determined by Coulter Counter analysis.Average particle size by weight signifies that 50 percent by weight ofthe particles are above a designated particle size and 50 percent byweight are less than a given particle size. At average particle sizesbelow about 2 microns, the degree of polishing substantially decreases,although there does remain some polishing action. When the averageparticle size increases above about 30 microns, and particularly whenabove about 40 microns, the polishing degrades to an abrasion of thetooth enamel surface. Also, when the average particle size is 40 micronsand above, there remains a gritty after-taste in the mouth of the user.This average particle size range of 2 to 30 microns is, therefore, apreferred range, with other sizes also being operable.

The silica gels of this invention are described in terms of their poresize distributions, adsorptive capacities, surface areas, pore volumes,average pore diameters, and bulk densities. The % solids of theadsorbent wet cake were determined by placing a representative 2 gsample on the pan of a CEM 910700 microwave balance and drying thesample to constant weight. The weight difference is used to calculatethe % solids content. Pack or tapped density is determined by weighing100.0 grams of product into a 250-mL plastic graduated cylinder with aflat bottom. The cylinder is closed with a rubber stopper, placed on thetap density machine and run for 15 minutes. The tap density machine is aconventional motor-gear reducer drive operating a cam at 60 rpm. The camis cut or designed to raise and drop the cylinder a distance of 2.25 in.(5.715 cm) every second. The cylinder is held in position by guidebrackets. The volume occupied by the product after tapping was recordedand pack density was calculated and expressed in g/ml.

The conductivity of the filtrate was determined utilizing an Orion Model140 Conductivity Meter with temperature compensator by immersing theelectrode epoxy conductivity cell (014010) in the recovered filtrate orfiltrate stream. Measurements are typically made at a temperature of15-20° C.

Surface area is determined by the BET nitrogen adsorption methods ofBrunaur et al., J. Am. Chem. Soc., 60, 309 (1938).

Accessible porosity has been obtained using nitrogenadsorption-desorption isotherm measurements. The BJH(Barrett-Joiner-Halender) model average pore diameter was determinedbased on the desorption branch utilizing an Accelerated Surface Area andPorosimetry System (ASAP 2010) available from Micromeritics InstrumentCorporation, Norcross, Ga. Samples were out gassed at 150-200° C. untilthe vacuum pressure was about 5 μm of Mercury. This is an automatedvolumetric analyzer at 77° K. Pore volume is obtained at pressureP/P₀=0.99. Average pore diameter is derived from pore volume and surfacearea assuming cylindrical pores. Pore size distribution (ΔV/ΔD) iscalculated using BJH method, which gives the pore volume within a rangeof pore diameters. A Halsey thickness curve type was used with pore sizerange of 1.7 to 300.0 nm diameter, with zero fraction of pores open atboth ends.

The N₂ adsorption and desorption isotherms were classified according tothe 1985 IUPAC classification for general isotherm types includingclassification of hysteresis to describe the shape and interconnectedness of pores present in the silicon based gel.

Adsorbent micropore area (S_(micro)) is derived from the Halsey isothermequation used in producing a t-plot. The t-plot compares a graph of thevolume of nitrogen absorbed by the adsorbent gel as compared with thethickness of the adsorbent layer to an ideal reference. The shape of thet-plot can be used to estimate the micropore surface area. Percentmicroporosity is then estimated by subtracting the external surface areafrom the total BET surface area, where S_(micron)=S_(BET)−S_(ext). Thus% BJH microporosity=S_(micro)/S_(BET)×100. The surface areas and porevolumes were determined by the nitrogen adsorption method described inBrunauer, Emmett, and Teller, 60 J. Am. Chem. Soc. 309 (1938) (known asBET). The selective determination of the nitrogen pore volume within agiven pore size range was made using the method described in Barrett,Joyner, and Halenda, 73 J. Am. Chem. Soc. 373 (1951).

Abrasivity was measured using a PERSPEX procedure. Such a methodentailed the utilization of a brush head brushing a PERSPEX plate incontact with a suspension of the silica gel in a sorbitol/glycerolmixture. A slurry composition was first formed of 2.5 grams of thesilica gel (or composite gel), 10.0 grams of glycerol, and 23.0 of a 70%sorbitol/30% water syrup. All components are weighed into a beaker anddispersed for 2 minutes at 1500 rpm using a simple stirrer. A 110 mm×55mm×3 mm sheet of standard PERSPEX Clear Cast Acrylic sheet grade 000,manufactured by Imperial Chemical Industries Ltd, was used for the test.The test is carried out using a modified Wet Abrasion Scrub TesterBrush. In addition a weight of 400 g is attached to the brush assembly,which weighs 145 g, to force the brush onto the PERSPEX plate. The brushhas a multi-tufted, flat trim nylon head with round ended filaments andmedium texture. A Galvanometer is calibrated using a 45° Plaspec glosshead detector and a standard (50% gloss) reflecting plate. TheGalvanometer reading is adjusted to a value of 50 under theseconditions. The reading of the fresh PERSPEX plate is then carried outusing the same reflectance arrangement. The fresh piece of PERSPEX wasthen fitted into a holder. Two cm³ of the dispersed silica, sufficientto lubricate fully the brushing stroke, was placed on the plate and thebrush head lowered onto the plate. The machine was switched on and theplate subjected to three hundred strokes of the weighted brush head. Theplate was removed from the holder and all the suspension was washed off.It was then dried and re-measured for its gloss value. The abrasionvalue was the difference between the unabraded value and the value afterabrasion.

To determine free fatty acid reductions in used cooking oils, initialand treated oils were analyzed by the official American Oil Chemists'Society methods for percent free fatty acids (Ca 5a-40).

Again, typical silica gel production methods require mixing finelydivided silica gel with an aqueous ammoniacal medium in order to providethe desired pore size diameter distribution. The method employed withinthis invention avoids the need for such ammonia utilization. As such,the costs of not only the extra ammoniacal solvent as well as the timeneeded for washing and then drying the ammoniated gels afterwards, isavoided. Hence, again, unexpectedly, the ability to produce silica gelsin an atypical gel production method as within this invention provides asignificantly more efficient procedure without compromising any poresize or surface area properties.

The gels and composite gels made through this process also exhibit muchsofter abrasive properties than standard gels produced through typicalgel production methods. Such new gels can be used within filter media(such as for absorption of noxious gases from air streams, removal offree fatty acids from cooking oils, as examples) or possibly as softabrasives in skin or tooth cleaning compositions.

In terms of filter applications, it has been realized that silica-basedcompositions make excellent gas filter media. However, little has beenprovided within the pertinent prior art that concerns the ability toprovide uptake and breakthrough levels by such filter media on apermanent basis and at levels that are acceptable for large-scale usage.Uptake basically is a measure of the ability of the filter medium tocapture a certain volume of the subject gas; breakthrough is anindication of the saturation point for the filter medium in terms ofcapture. Thus, it is highly desirable to find a proper filter mediumthat exhibits a high uptake (and thus quick capture of large amounts ofnoxious gases) and long breakthrough times (and thus, coupled withuptake, the ability to not only effectuate quick capture but alsoextensive lengths of time to reach the filter capacity). The standardfilters in use today are limited for noxious gases, such as ammonia, toslow uptake and relatively quick breakthrough times. There is a need todevelop a new filter medium that increases uptake and breakthrough, as aresult.

The closest art concerning the removal of gases such as ammoniautilizing a potential silica-based compound doped with a metal is taughtwithin WO 00/40324 to Kemira Agro Oy. Such a system, however, isprimarily concerned with providing a filter media that permitsregeneration of the collected gases, presumably for further utilization,rather than permanent removal from the atmosphere. Such an ability toeasily regenerate (i.e., permit release of captured gases) such toxicgases through increases of temperature or changes in pressureunfortunately presents a risk to the subject environment. To thecontrary, an advantage of a system as now proposed is to provideeffective long-duration breakthrough (thus indicating thorough andeffective removal of unwanted gases in substantially their entirety froma subject space over time), as well as thorough and effective uptake ofsubstantially all such gases as indicated by an uptake measurement. TheKemira reference also is concerned specifically with providing a drymixture of silica and metal (in particular copper I salts, ultimately),which, as noted within the reference, provides the effective uptake andregenerative capacity sought rather than permanent and effective gas(such as ammonia) removal from the subject environment.

In a typical restaurant frying operation, large quantities of ediblecooking oils or fats are heated in vats to temperatures of from about315 to about 400° F. or more, and the food is immersed in the oil or fatfor cooking. During repeated use of the cooking oil or fat the highcooking temperatures, in combination with water from the food beingfried, cause the formation of free fatty acids (or FFA). An increase inthe FFA decreases the oil's smoke point and results in increasing smokeas the oil ages. Increased FFA content also causes excessive foaming ofthe hot fat and contributes to an undesirable flavor or development ofdark color. Any or all of these qualities associated with the fat candecrease the quality of the fried food.

Industrial frying operations involve the frying of large amounts of foodfor delayed consumption. Often, this is a continuous operation with thefood being carried through the hot oil via a conveyor. Industrial fryersof meat and poultry must follow the strict FDA guidelines in terms ofthe length of time oils and fats may be used for deep fat fryingpurposes. Suitability of further or prolonged use can be determined fromthe degree of foaming during use or from color and odor of the oiland/or fat or from the flavor of the resultant fried food madetherefrom. Fat or oil should be discarded when it foams over a vessel'sside during cooking, or when its color becomes almost black as viewedthrough a colorless glass container. Filtering of used oil and/or fat ispermitted, however, to permit further use, as well as adding fresh fatto a vessel and cleaning frying equipment regularly. Large amounts ofsediment and free fatty acid content in excess of 2 percent are usualindications that frying fats are unwholesome and require reconditioningor replacement. Most industrial fryers use the 2% free fatty acid (FFA)limit, or less if mandated by their customers, for poultry as their mainspecification for oil quality, regardless of the food being fried.

In addition to hydrolysis, which forms free fatty acids, there occursoxidative degeneration of fats which results from contact of air withhot oil, thereby producing oxidized fatty acids (or OFA). Heatingtransforms the oxidized fatty acids into secondary and tertiaryby-products which may cause off-flavors and off-odors in the oil andfried food. Caramelization also occurs during the use of oil over aperiod of time, resulting in a very dark color of the oil which,combined with other by-products, produces dark and unappealing friedfoods. Because of the cost resulting from the replacing of the cookingoils and fats after the use thereof, the food industries have searchedfor effective and economical ways to slow degradation of fats and oilsin order to extend their usable life. The silica gels (particularly thecaustic gels and composite gels) of this invention exhibit excellentability to revoke FFA from such used cooking oils.

These novel silica gels may be combined with any number of otherabsorbents and/or additives for the purpose of permitting greaterversatility in removing undesirable materials from certain streams andused oils. Thus, activated carbons, other silica materials (such asmetal-doped precipitated silicas or silica gels, magnesium silicates,and the like) may be included within the same filter apparatus for sucha purpose.

After production, if filter applications are desired, the gel orcomposite gel may then be compressed or compacted to form pellets ofadequate structural integrity to withstand the compressive forces andabrasions experienced in a fixed bed filter without being crushed orreduced to fines that would reduce the efficiency of the filter. Variouscompression molding methods that provide the necessary degree ofcompaction of the mixture may be employed in the method of thisinvention. Suitable apparatus that may be used to compress the mixtureincludes, for example, compactors, briquetters, extruders, hydraulicpresses, rotary mold presses, and the like. The size and/or shape of thepellets can be adapted to suit the catalytic application. The pelletsmay be circular or polygonal (either regular or irregular) incross-section and may vary in diameter from about 1/16 to about 5/16 ofan inch and from about ⅛ to about ½ of an inch in length. Pellets ofsimilar size may be prepared, for example, in the form of saddles,pillows, hollow cylinders, or doughnuts. The term pellets is intended tocover compacted articles prepared by this invention regardless of theirshape, whether solid or with a hole therein, and regardless of themethod of compacting and includes pellets, extrusions, tablets,briquettes, and other shapes which have been subjected to the requisitecompacting. Preferably, the mixture is compressed to form solid,cylindrical pellets.

PREFERRED EMBODIMENTS OF THE INVENTION

The following non-limiting examples are provided as guidelines oftypical inventive production methods as well as inventive silica gelsand composite gels themselves.

Silicic Acid Gel Production, both Acidic and Caustic

EXAMPLE I Silicic Acid Gel

1867 cc of water were introduced into a 1 gallon stainless vessel. ThepH thereof was adjusted to about 4 with H₂SO₄ and the formulation wasthen heated to 90° C. In a 1.5 liter reactor, 153.2 cc of roomtemperature sulfuric (11.4 wt %) acid were then introduced undersufficient agitation to stir with minimal splashing (˜120 RPM). Sodiumsilicate (3.3 molar ratio, 24.7 wt %) was then added thereto at roomtemperature in two stages. In the first stage, silicate addition was ata rate of 11.4 cc/min until the resultant pH was close to 2.5. After 10minutes, the RPM was raised to 250 and gradually increase to 300 over aperiod of several minutes. At that point, the second stage silicateaddition was initiated at a rate of 1.7 cc/min until the resultant pHlevel was about 2.85. The silicate addition was then stopped and the pHthereof was manually adjusted to 3.00.

This reactor batch was then transferred into a 1-gallon vesselcontaining hot water. The temperature was then maintained at about 90°C. with no agitation for at least 45 minutes. The resultant gel slurrywas then vacuum filtered with filter paper and 4000 cc of water with asubsequent air purge for 30 minutes after the wet gel cake cracked. Theresulting gel wet cake was dried in an oven overnight.

EXAMPLE II Caustic Gel

1867 cc of water were introduced into a 1 gallon stainless vessel. 10 ccof 10% NaOH solution were added to the water and heated to 90° C. Theremaining steps were the same as followed in the EXAMPLE 1, above. Theresultant gel was caustic in nature, however, due to the presence ofsodium hydroxide within the reaction.

EXAMPLE III Silicic Acid Gel

The same method was followed for EXAMPLE 1, above, except that the pH ofthe resultant product after the second stage of silicate addition wasadjusted to 3.81.

The reactor batch was then transferred into a 1-gallon vessel containinghot water, all while maintaining the temperature at about 90° C. with noagitation initially. After 22 minutes, the aged reactor batch wasagitated for 1 minute, as well as at the 44 minute point for 1 minute,both at 300 rpm. The resultant gel slurry was then vacuum filtered withfilter cloth and 4000 cc of water, and air purged for 30 minutes afterthe wet gel cake cracked. The resulting gel wet cake was dried in theoven overnight.

EXAMPLE IV Silicic Acid Gel, pH 1.75

A 2-gallon ambient reactor was charged with 2000 mls of 11.4% Sulfuricacid (sg 1.074). Sodium silicate [24.7% (3.3 MR)] was then added theretoat a rate of 40 mls/min to attain a pH of 1.75. The resulting sol wasthen placed in an oven maintained at 75° C. remained undisturbed forapproximately 3 hours until fully gelled. The gel was then crumbled andwashed by feeding water into the bottom inlet of a wash vessel andhaving the salt wash water overflow at the top. During the washing step,the gel was agitated periodically to effect better desalting to aconductivity of <1000 μS/cm². The resultant washed gel was then furtherdewatered by siphoning off the excess water and filtering the solidsfollowing by oven drying at 105° C. The dried gel can then be milled orcompacted into granules.

EXAMPLE V Acidic Gel, 400 Gallon Reactor

900 liters of water was introduced into a filter feed tank. The pHthereof was adjusted to 4 with 11.4% sulfuric acid and the resultantsolution was then heated to 90° C. using steam sparging. The feed tankwas then filled completely with cold water and cooled to about 30° C.

In a 400 gallon reactor, 150 liters of room temperature sulfuric (11.4wt %) acid was introduced under sufficient agitation to stir, but withminimal splashing. Sodium silicate addition (3.3 molar ratio, 24.7 wt %)was then started at room temperature in two stages. The rate of silicateaddition in the first stage was 3 liters/min until the pH level wasabout 2.5. The second stage of silicate addition then began at a rate of1.5 liters/min until a pH of about 2.85 was reached. The silicateaddition then stopped and the pH of the resultant batch was manuallyadjusted to 3.00.

The reactor batch was then pumped into the filter feed tank at amaintained temperature of about 90° C. without any agitation initially.After 22 minutes, the batch in the feed tank was agitated once for 1minute, and again at the 44 minute point for 1 minute (both at 500 rpm).Immediately after the second agitation, the resultant gel slurry waswashed and filtered with a filter press (EIMCO) until the filtrateconductivity was below 3000 μmho. The resultant product was then airpurged for 10, and then the resultant wet cake was oven dried.

EXAMPLE VI Caustic Gel via Silicate Addition

The same method as in EXAMPLE 1, above, was followed to form the reactorbatch with a manually adjusted pH of 3.00. Then, the reactor batch wastransferred in to a 1-gallon vessel containing hot water whilemaintaining the temperature at about 90° C. under no agitationinitially. After 22 minutes, the aged batch was agitated for 1 minute at500 rpm, followed by the introduction of 30 cc of 24.7% sodium silicate(3.3 MR). This new batch was then further agitated 22 minutes after thesodium silicate introduction for 1 minute at 500 rpm. The resultantcaustic gel slurry was then vacuum filtered with filter cloth and 4000cc of water and then air purged for 30 minutes after the wet gel cakecracked. The resulting gel wet cake was dried in an oven overnight.

EXAMPLE VII Silicic Acid Gel

1020 cc of water were introduced within a 1-gallon stainless vessel andthe pH thereof was then adjusted to about 4 with H₂SO₄. This aqueoussolution was then heated to 90° C. In a 1.5 liter reactor, 153.2 cc ofroom temperature sulfuric (11.4 wt %) acid was then introduced undersufficient agitation to stir, but with minimal splashing (˜120 RPM).Sodium silicate (3.3 molar ratio, 24.7 wt %) addition at roomtemperature was then initiated in two stages. The first stage involved asodium silicate addition at a rate of 11.4 cc/min until the pH level wasabout 2.5. After 10 minutes, the RPM was raised to 250 and graduallyincreased to 300 over a period of several minutes. Thereafter, thesecond stage silicate addition began at a rate of 1.7 cc/min untilpH≈2.85 is reached, at which time silicate addition finished. The pH ofthe resultant batch was then manually adjusted to 3.00.

The resultant reactor batch was then transferred into a 1-gallon vesselcontaining hot water and maintained at a temperature of about 90° C.under no agitation initially. After 22 minutes, the aged reactor batchwas agitated for 1 minute, as well as at the 44 minute point for 1minute, both at 300 rpm. The resultant gel slurry was then vacuumfiltered with filter cloth and 5000 cc of water and air purged for 30minutes after the wet gel cake cracked. The resulting gel wet cake wasdried in the oven overnight.

EXAMPLE VIII Caustic Gel via Initial Silicate Presence

1020 cc of water were introduced within a 1-gallon stainless vessel andthe pH thereof was then adjusted via the introduction of 10 cc of 24.7%sodium silicate solution. This aqueous solution was then heated to 90°C. In a 1.5 liter reactor, 153.2 cc of room temperature sulfuric (11.4wt %) acid was then introduced under sufficient agitation to stir, butwith minimal splashing (˜120 RPM). Sodium silicate (3.3 molar ratio,24.7 wt %) addition at room temperature was then initiated in twostages. The first stage involved a sodium silicate addition at a rate of11.4 cc/min until the pH level was about 2.5. After 10 minutes, the RPMwas raised to 250 and gradually increased to 300 over a period ofseveral minutes. Thereafter, the second stage silicate addition began ata rate of 1.7 cc/min until pH≈2.85 is reached, at which time silicateaddition finished. The pH of the resultant batch was then manuallyadjusted to 3.00.

The resultant reactor batch was then transferred into a 1-gallon vesselcontaining hot water and maintained at a temperature of about 90° C.under no agitation initially. After 22 minutes, the aged reactor batchwas agitated for 1 minute, as well as at the 44 minute point for 1minute, both at 300 rpm. The resultant gel slurry was then vacuumfiltered with filter cloth and 5000 cc of water and air purged for 30minutes after the wet gel cake cracked. The resulting gel wet cake wasdried in the oven overnight.

EXAMPLE IX Caustic Gel

The same method as in EXAMPLE VIII was followed except that 5 cc of 10%NaOH solution were added to the initial aqueous solution, rather than 10cc of 24.7% sodium silicate.

EXAMPLE X Caustic Gel

The same method as in EXAMPLE IX was followed except that 12 cc of 10%NaOH was added to the initial aqueous solution.

EXAMPLE XI Caustic Gel

1020 cc of water were introduced within a 1-gallon stainless vessel andthe pH thereof was then adjusted via the introduction of 10 cc of 24.7%sodium silicate solution. This aqueous solution was then heated to 90°C. In a 1.5 liter reactor, 153.2 cc of room temperature sulfuric (11.4wt %) acid was then introduced under sufficient agitation to stir, butwith minimal splashing (˜120 RPM). Sodium silicate (3.3 molar ratio,24.7 wt %) addition at room temperature was then initiated in twostages. The first stage involved a sodium silicate addition at a rate of11.4 cc/min until the pH level was about 2.5. After 10 minutes, the RPMwas raised to 250 and gradually increased to 300 over a period ofseveral minutes. Thereafter, the second stage silicate addition began ata rate of 1.7 cc/min until pH≈2.85 is reached, at which time silicateaddition finished. The pH of the resultant batch was then manuallyadjusted to 3.00.

The resultant reactor batch was then transferred into a 1-gallon vesselcontaining hot water and maintained at a temperature of about 90° C.under no agitation initially. After 22 minutes, the aged reactor batchwas agitated for 1 minute, as well as at the 44 minute point for 1minute, both times at 300 rpm. The resultant gel slurry was then vacuumfiltered with filter cloth and 5000 cc of water and air purged for 30minutes after the wet gel cake cracked. The resulting gel wet cake wasdried in the oven overnight.

EXAMPLE XII Caustic Gel

10 grams of the resultant caustic gel from EXAMPLE IX were slurried in200 ml water, to which a sufficient amount of 10% NaOH was added toraise the slurry pH to about 7.26. After the resultant slurry was thendried, the pH was measured to be about 7.31. This material was thencombined with an additional 5 grams of the EXAMPLE IX gel, reslurried,adjusted to a pH of about 9.32, and dried.

EXAMPLE XIII Silicic Acid Gel, 2.5 MR

1020 cc of water were introduced within a 1-gallon stainless vessel andthe pH thereof was then adjusted to about 4 with H₂SO₄. This aqueoussolution was then heated to 90° C. In a 1.5 liter reactor, 202.9 cc ofroom temperature sulfuric (11.4 wt %) acid was then introduced undersufficient agitation to stir, but with minimal splashing (˜120 RPM).Sodium silicate (2.5 molar ratio, 30.0 wt %) addition at roomtemperature was then initiated in two stages. The first stage involved asodium silicate addition at a rate of 7.1 cc/min until the pH level wasabout 2.5. After 10 minutes, the RPM was raised to 250 and graduallyincreased to 300 over a period of several minutes. Thereafter, thesecond stage silicate addition began at a rate of 1.5 cc/min untilpH≈2.85 is reached, at which time silicate addition finished. The pH ofthe resultant batch was then manually adjusted to 3.00.

The resultant reactor batch was then transferred into a 1-gallon vesselcontaining hot water and maintained at a temperature of about 90° C.under no agitation initially. After 22 minutes, the batch was agitatedfor 1 minute, as well as at the 44 minute point for 1 minute, both at500 rpm. Immediately thereafter, the resultant gel slurry was thenvacuum filtered with filter cloth and 5000 cc of water and air purgedfor 30 minutes after the wet gel cake cracked. The resulting gel wetcake was dried in the oven overnight.

EXAMPLE XIV Caustic Gel

1020 cc of water were introduced within a 1-gallon stainless vessel andthe pH thereof was then adjusted via the introduction of 10 cc of 24.7%sodium silicate solution. This aqueous solution was then heated to 90°C. In a 1.5 liter reactor, 153.2 cc of room temperature sulfuric (11.4wt %) acid was then introduced under sufficient agitation to stir, butwith minimal splashing (˜120 RPM). Sodium silicate (3.3 molar ratio,24.7 wt %) addition at room temperature was then initiated in twostages. The first stage involved a sodium silicate addition at a rate of11.4 cc/min until the pH level was about 2.5. After 10 minutes, the RPMwas raised to 250 and gradually increased to 300 over a period ofseveral minutes. Thereafter, the second stage silicate addition began ata rate of 1.7 cc/min until pH≈2.85 is reached, at which time silicateaddition finished. The pH of the resultant batch was then manuallyadjusted to 3.00.

The resultant reactor batch was then transferred into a 1-gallon vesselcontaining hot water and maintained at a temperature of about 90° C.under constant agitation of 50 rpm for 45 minutes. The resultant gelslurry was then vacuum filtered with filter cloth and 5000 cc of waterand air purged for 30 minutes after the wet gel cake cracked. Theresulting gel wet cake was dried in the oven overnight.

EXAMPLE XV Sodium Caustic Gel, 30 Gallon Reactor

79 liters of water were introduced into filter feed tank. 84 cc of 50%NaOH were then added thereto and the resultant solution was heated to90° C.

In a 30 gallon reactor, 13 liters of room temperature sulfuric (11.4 wt%) acid was then introduced under sufficient agitation to stir, but withminimal splashing (˜120 RPM). Sodium silicate (3.3 molar ratio, 24.7 wt%) addition at room temperature was then initiated in two stages. Thefirst stage involved a sodium silicate addition at a rate of o.26liters/min until the pH level was about 2.5. Thereafter, the secondstage silicate addition began at a rate of 0.13 liters /min untilpH≈2.85 is reached, at which time silicate addition finished. The pH ofthe resultant batch was then manually adjusted to 3.00.

The resultant reactor batch was then transferred into a filter feed tankand maintained at a temperature of about 90° C. under no agitationinitially. After 22 minutes, the aged reactor batch was agitated for 1minute, as well as at the 44 minute point for 1 minute, both at 300 rpm.The resultant gel slurry was then washed and filtered with a filterpress (EIMCO), until the filtrate conductivity was below 3000 μmho. Thissample was then air purged for 12 minutes and the resultant wet gel cakewas spin flash dried (APV) until the cake cracked.

EXAMPLE XVI Sodium Caustic Gel, 400 Gallon Reactor

1200 liters of water were introduced into a filter feed tank. 1.4 litersof 50% NaOH solution was added thereto and the resultant solution wasthen heated to 90° C. using steam sparging. The final volume wasapproximately 1350 liters within the filter feed tank.

In a 400 gallon reactor, 225 liters of room temperature sulfuric (11.4wt %) acid was introduced under sufficient agitation to stir, but withminimal splashing. Sodium silicate addition (3.3 molar ratio, 24.7 wt %)was then started at room temperature in two stages. The rate of silicateaddition in the first stage was 4.5 liters/min until the pH level wasabout 2.5. The second stage of silicate addition then began at a rate of2 liters/min until a pH of about 2.85 was reached. The silicate additionthen stopped and the pH of the resultant batch was manually adjusted to3.00.

The reactor batch was then pumped into the filter feed tank at amaintained temperature of about 90° C. without any agitation initially.After 22 minutes, the batch in the feed tank was agitated once for 1minute, and again at the 44 minute point for 1 minute (both at 500 rpm).Immediately after the second agitation, the resultant gel slurry waswashed and filtered with a filter press (EIMCO) until the filtrateconductivity was below 3000 μmho. The resultant product was then airpurged for 10, and then the resultant wet cake was then flash dried(Aljet ring flash dryer).

EXAMPLE XVII Acidic Gel, 30 Gallon Reactor

79 liters of water were introduced into a filter feed tank. The pH wasadjusted to 4 with sulfuric acid and the solution was heated to 90° C.Separately, in a 30 gallon reactor, 13 liters of room temperaturesulfuric (11.4 wt %) acid was then added under sufficient agitation tostir with minimized splashing. Sodium silicate addition (3.3 molarratio, 24.7 wt %) was then started at room temperature in two stages.The rate of silicate addition in the first stage was 0.26 liters/minuntil the pH level was about 2.5. The second stage of silicate additionthen began at a rate of 0.13 liters/min until a pH of about 2.85 wasreached. The silicate addition then stopped and the pH of the resultantbatch was manually adjusted to 3.00.

The reactor batch was then pumped into the filter feed tank at amaintained temperature of about 90° C. without any agitation initially.After 22 minutes, the batch in the feed tank was agitated once for 1minute, and again at the 44 minute point for 1 minute (both at 500 rpm).Immediately after the second agitation, the resultant gel slurry waswashed and filtered with a filter press (EIMCO) until the filtrateconductivity was below 3000 μmho. The resultant product was then airpurged for 12 minutes and the resulting gel wet cake was spin flashdried (APV).

EXAMPLE XVIIA

The same method was followed as in EXAMPLE XVIII, above, except that theresulting gel wet cake was oven dried.

EXAMPLE XVIII Sodium Caustic Gel, 30 Gallon Reactor

79 liters of water were introduced into a filter feed tank. 84 cc of 50%NaOH solution were then added thereto and the solution was then heatedto 90° C. In a 30 gallon reactor, 13 liters of room temperature sulfuric(11.4 wt %) acid were then introduced under sufficient agitation tostir, but with minimal splashing (as above). Sodium silicate addition(3.3 molar ratio, 24.7 wt %) was then started at room temperature in twostages. The rate of silicate addition in the first stage was 0.26liters/min until the pH level was about 2.5. The second stage ofsilicate addition then began at a rate of 0.13 liters/min until a pH ofabout 2.85 was reached. The silicate addition then stopped and the pH ofthe resultant batch was manually adjusted to 3.00.

The reactor batch was then pumped into the filter feed tank at amaintained temperature of about 90° C. without any agitation initially.After 22 minutes, the batch in the feed tank was agitated once for 1minute, and again at the 44 minute point for 1 minute (both at 500 rpm).Immediately after the second agitation, the resultant gel slurry waswashed and filtered with a filter press (EIMCO) until the filtrateconductivity was below 3000 μmho. The resultant product was then airpurged for 12 minutes and the resulting gel wet cake was spin flashdried (APV).

EXAMPLE XIX Sodium Caustic Gel, 400 Gallon Reactor

800 liters of water was introduced into a filter feed tank. 0.95 litersof 50% NaOH solution was added thereto and the resultant solution wasthen heated to 90° C. using steam sparging. The final volume wasapproximately 960 liters within the filter feed tank.

In a 400 gallon reactor, 150 liters of room temperature sulfuric (11.4wt %) acid was introduced under sufficient agitation to stir, but withminimal splashing. Sodium silicate addition (3.3 molar ratio, 24.7 wt %)was then started at room temperature in two stages. The rate of silicateaddition in the first stage was 3 liters/min until the pH level wasabout 2.5. The second stage of silicate addition then began at a rate of1.5 liters/min until a pH of about 2.85 was reached. The silicateaddition then stopped and the pH of the resultant batch was manuallyadjusted to 3.00.

The reactor batch was then pumped into the filter feed tank at amaintained temperature of about 90° C. without any agitation initially.After 22 minutes, the batch in the feed tank was agitated once for 1minute, and again at the 44 minute point for 1 minute (both at 500 rpm).Immediately after the second agitation, the resultant gel slurry waswashed and filtered with a filter press (EIMCO) until the filtrateconductivity was below 3000 μmho. The resultant product was then airpurged for 10, the resulting gel wet cake was diluted to about 7-8%solids, and then the resultant low solids wet cake was spray dried.

Composite Gel Synthesis EXAMPLE XX Calcium Co-Gel, 30 Gallon Reactor

79 liters of water were introduced into a filter feed tank. 192 cc of aslaked lime slurry (16.4% by weight) solution were then added theretoand the solution was then heated to 90° C. In a 30 gallon reactor, 13liters of room temperature sulfuric (11.4 wt %) acid were thenintroduced under sufficient agitation to stir, but with minimalsplashing (as above). Sodium silicate addition (3.3 molar ratio, 24.7 wt%) was then started at room temperature in two stages. The rate ofsilicate addition in the first stage was 0.26 liters/min until the pHlevel was about 2.5. The second stage of silicate addition then began ata rate of 0.13 liters/min until a pH of about 2.85 was reached. Thesilicate addition then stopped and the pH of the resultant batch wasmanually adjusted to 3.00.

The reactor batch was then pumped into the filter feed tank at amaintained temperature of about 90° C. without any agitation initially.After 22 minutes, the batch in the feed tank was agitated once for 1minute, and again at the 44 minute point for 1 minute (both at 500 rpm).Immediately after the second agitation, the resultant gel slurry waswashed and filtered with a filter press (EIMCO) until the filtrateconductivity was below 3000 μmho. The resultant product was then airpurged for 12 minutes and the resulting gel wet cake was spin flashdried (APV).

EXAMPLE XXI Magnesium Co-gel, 30 Gallon Reactor

79 liters of water were introduced into a filter feed tank. 62.2 cc of50.8% Mg(OH)₂ slurry were then added thereto and the solution was thenheated to 90° C. In a 30 gallon reactor, 13 liters of room temperaturesulfuric (11.4 wt %) acid were then introduced under sufficientagitation to stir, but with minimal splashing (as above). Sodiumsilicate addition (3.3 molar ratio, 24.7 wt %) was then started at roomtemperature in two stages. The rate of silicate addition in the firststage was 0.26 liters/min until the pH level was about 2.5. The secondstage of silicate addition then began at a rate of 0.13 liters/min untila pH of about 2.85 was reached. The silicate addition then stopped andthe pH of the resultant batch was manually adjusted to 3.00.

The reactor batch was then pumped into the filter feed tank at amaintained temperature of about 90° C. without any agitation initially.After 22 minutes, the batch in the feed tank was agitated once for 1minute, and again at the 44 minute point for 1 minute (both at 500 rpm).Immediately after the second agitation, the resultant gel slurry waswashed and filtered with a filter press (EIMCO) until the filtrateconductivity was below 3000 μmho. The resultant product was then airpurged for 12 minutes and the resulting gel wet cake was spin flashdried (APV).

EXAMPLE XXII Magnesium Co-gel, 400 Gallon Reactor

800 liters of water was introduced into a filter feed tank. 0.72 litersof 50.8% Mg(OH)₂ slurry were then added thereto and the solution wasthen heated to 90° C. using steam sparging. The final volume of thecontents of the feed tank were about 960 liters.

In a 400 gallon reactor, 150 liters of room temperature sulfuric (11.4wt %) acid was introduced under sufficient agitation to stir, but withminimal splashing. Sodium silicate addition (3.3 molar ratio, 24.7 wt %)was then started at room temperature in two stages. The rate of silicateaddition in the first stage was 3 liters/min until the pH level wasabout 2.5. The second stage of silicate addition then began at a rate of1.5 liters/min until a pH of about 2.85 was reached. The silicateaddition then stopped and the pH of the resultant batch was manuallyadjusted to 3.00.

The reactor batch was then pumped into the filter feed tank at amaintained temperature of about 90° C. without any agitation initially.After 22 minutes, the batch in the feed tank was agitated once for 1minute, and again at the 44 minute point for 1 minute (both at 500 rpm).Immediately after the second agitation, the resultant gel slurry waswashed and filtered with a filter press (EIMCO) until the filtrateconductivity was below 3000 μmho. The resultant product was then airpurged for 10, the resultant wet cake wash and diluted to a solidscontent of 7-8%, and then the resultant wet cake was spray dried.

COMPARATIVE EXAMPLE Comparative Caustic SG 408

15 grams of SG 408 (silica gel product from W. R. Grace) was slurried in285 ml water, to which a sufficient amount of 10% NaOH was added toraise the slurry pH to about 9.02. After the resultant slurry was thendried, the pH was measured to be about 9.6.

Sample Analyses—Chemical and Physical Characteristics

Selected samples form the Examples above were then analyzed fordifferent properties, including pore volume and diameter, hysteresis,surface area, washing times (to determine the length of time required toremove excess salts from the produced gels), abrasivity, and oilfilitration capability, all in accordance with the test protocols listedpreviously. The results are in tabular form as follows:

TABLE I Chemical Properties of Oven-Dried Gel Samples Surface Inventivearea Pore volume Pore diameter Example # (m²/g) (cc/g) (Å) HysteresisNa₂SO₄ I 715.4 0.42 23.2 Small 9.3% II 630.5 0.56 34.7 Medium 5.9% III348 0.83 91 Large 1.1% VI 311 0.695 89.5 Medium 4.45% 

TABLE II Chemical Properties of Gel Made by Modified Procedures.Inventive Total Pore Average Pore Example # 5% pH BET SA (m²/g) volume(cc/g) diameter (Å) VII 4.42 651 0.38 23.6 X 9.73 306 0.38 49.6 XI 9.24488.3 0.77 63.1 XII 9.26 359.5 0.91 101.2

TABLE III Comparative Commercial Gel and Caustic Treated Gel ExamplesComparative Example Sample SG 408¹(acidic) SG 408 (caustic treated) 5%pH 3.5 9.6 BET SA (m²/g) 651 367.9 Total Pore volume (cc/g) 0.41 0.37Average Pore diameter (Å) 21.8 40.2 ¹Silica Gel from W.R. Grace Co.

The gels of Table I show similar properties to the commercial gel ofTable III. As well, the caustic gels of Table II (examples X, XI, andXII) exhibited drastically different pore volumes and pore diametersthan the simple post-gel caustic treatment of the commercially availablegel, showing how the novel caustic gel production method permitsproduction of such novel gel materials as well.

TABLE IV Acidic Gels Produced with Different Molar Ratio SilicateReactants Inventive Example # VII XIII 5% pH 4.42 4.72 BET SA (m²/g) 651719.1 Total Pore volume (cc/g) 0.38 0.42 Average Pore diameter (Å) 23.623.4

Even with different mole ratio silicate reactants, the novel methodprovided similar gels as chemically analyzed to those availablecommercially as well.

TABLE V Washing Time Comparisons for Quick Salt Removal ml. Volume ml.of Volume Conduc- % *approximate water of tivity Na₂SO₄ filtrationInventive In drop Wash of in dry time Example # Tank Water FiltrateProduct (cake crack) VII 1020.6 5000 3.23 mS 3.12% 38 min. VIII 10205000 1.02 mS 2.32/2.34% 5 minutes IX 1020 5000  778 uS 0.85% 7 min 30sec.

These results show the benefits in terms of shortened washing timesthereby providing a very efficient procedure for gel manufacture.

TABLE VI Abrasivity Comparison of Acidic and Caustic gels AverageParticle Avg. Inventive Size Plate Start Avg. End Gloss Example #(microns) I.D. Gloss Gloss Change VII 34.28 1A 89 66.2 22.8 ″ ″ 1B 88.967.2 21.7 ″ ″ 1C 89.4 68.1 21.3 ″ ″ 1D 89.2 68 21.2 ″ ″ Average 89.12567.375 Avg. 21.75 Delta Gloss = XIV 40.36 2A 89.5 88.9  0.6 ″ ″ 2B 89.586.8  2.7 ″ ″ 2C 89.8 88.2  1.6 ″ ″ 2D 89.9 89.1  0.8 ″ ″ Average 89.67588.25 Avg. 1.425 Delta Gloss =

TABLE VII Abrasion Test Comparing New Gel and Commercial Gel (SG 408)Average Particle Avg. Sample Size Mesh Plate Start Avg. End Gloss I.D.(microns) Size I.D. Gloss Gloss Change SG-408 15.3 T-325 1A 90.6 72.717.9 ″ ″ ″ 1B 90.2 73.6 16.6 ″ ″ ″ 1C 90.4 72.8 17.6 ″ ″ ″ 1D 90.7 74.116.6 ″ Average 90.475 73.3 Avg. 17.175 Delta Gloss = Inventive 16.3T-325 2A 91.1 89.9  1.2 Example V Inventive ″ ″ 2B 90.8 88.5  2.3Example V Inventive ″ ″ 2C 90.3 88.9  1.4 Example V Inventive ″ ″ 2D90.5 88.9  1.6 Example V Inventive Average 90.675 89.05 Avg. 1.625Example V Delta Gloss =

Thus, gels of differing hardness (abrasivity) are possible via the novelmanufacturing methods. As well, much softer gels from those availablecommercially are provided through these novel methods, particularlythose caustic in nature. When coupled with the chemical propertieslisted above, it is evident that the caustic gels are totally differentfrom such a commercially available gel.

TABLE VIII Comparison of Gels Made Through Different Drying StepsInventive pH Pore volume Surface area Pore diameter Na₂SO₄ Example # drycc/g m²/g Å % XIV 9.2 0.984 294.6 133.6 1.22 XV 8 1.12 425.5 105.6 1.65XVI 8.7 1.32 444 118.8 2.5 XVIII 5.5 0.63 708.9 35.4 3.27 XVIIIA 5.50.46 676 27.4 3.27

TABLE IX Comparison of Gels Made Through Different Drying StepsInventive Example # XVIII XXI XIX XXII Reactor (gallon) 30 400 30 400BET SA (m²/g) 243 279.4 444 329.6 Total Pore 0.92 1.16 1.32 1.23 volume(cc/g) Average Pore 151.8 165.8 118.8 149.3 diameter (Å)

As compared to acidic gel, which has low pore volume (0.63 cc/g), smallpore size and high surface area (709 m²/g), both caustic gel andcomposite gel are basic and have higher pore volume, larger pore sizesand lower surface area. The composite gel exhibits an even higher totalpore volume than the caustic gel (greater than 1 cc/g), whilesurprisingly and simultaneously exhibiting a larger surface area as well(greater than 350 m²/g). As such, it is highly surprising that such aresult is reached since it is counterintuitive that an increase in porevolume will result in a resultant increase in surface area as well.Generally, there will be a correlated reduction in surface area as porevolume increases. It is not understood how this result has beenachieved, but at least the ability to control silica gel morphologythrough caustic pH exposure (rather than high temperature aging) hasbeen shown through these examples. The water insoluble (e.g., calciumhydroxide) reactants provide significant differences from the watersoluble types (e.g., sodium hydroxide) in terms of the final silica gelproducts made therefrom within the inventive method.

The biggest difference in properties between the caustic and compositegel is the relationship between pore diameter, pore volume and surfacearea. For caustic gel, both pore volume and diameter increase with largedecrease of surface area. While the composite gels seem to maximize thepore volume, and have less impact on pore diameter and surface area. Thedifferent drying steps that can be followed thus provide possibleavailability of more efficient drying methods to produce effective gelmaterials.

Samples Analyses—Oil Filtration Capability

Testing was then undertaken to analyze the ability of certain compositeand caustic gels to filter free fatty acids (FFA) from used cookingoils. The general method followed was to measure a known quantity ofabused cooking oil, either highly abused (generally defined as oil usedat typical frying temperatures more than four frying cycles) or lightlyabused (generally defined as oil used at typical frying temperatures forone frying cycle) and heat to 310-330° F.; add a predetermined amount ofabsorbent (2-6%) and stir for 5 minutes; continue heating and stirringfor exactly 5 minutes, after which filter the media through a 70 cm #4Whatman filter paper supported on a appropriate Buchner funnel; time thefiltration to get an indication of filtration rate from initial pouringto the disappearance of the excess oil from the bed under maximumvacuum; and collect the filtrate and measure the transmittance at 589 nmusing 97% glycerin as a 100% transmittance standard. The results were asfollows:

TABLE X Oil filtration data - Highly Abused Cooking Oil Total BET PoreMedian Particle Surface Vol Pore Dia Size % Color Sample Area m2/g cm3/g(angstroms) (microns) 5% pH % T Change Control (oil n/a n/a n/a n/a n/a44.4 n/a alone) Britesorb ®¹ 535 1.20 12 40 8.7 74 68 (6% usage)Magnesol ®² 400 0.88 95 * 8.5 69.8 57 (6% usage) SG 408 (6% 750 0.35 <2560 6.5 51.4 16 usage) Inv. Ex. IV 525 0.27 21 60 — 54.2 22 (6% usage)Inv. Ex. 216 1.05 190 40 8.5 70.2 58 XVI (6% usage) Inv. Ex. 330 1.23149 40 8.5 69.8 57 XVII (6% usage) Inv. Ex. 216 1.05 190 40 — 61.8 39XVI_(4% usage) ¹A silica gel material from PQ Corporation ²MagnesiumSilicate from The Dallas Group * Particle Sizes are listed commerciallyas between 20 and 75 microns — no measurements taken

TABLE XI Oil filtration data - Lightly Abused Cooking Oil Sample % T %Color Change % Free Fatty Acid Control (oil alone) 60.8 n/a 0.880Britesorb ® (6% 77.2 27 0.2991 usage) Magnesol ® (6% 75.2 24 0.6844usage) Inv. Ex. XIX (6% 74.2 22 0.619 usage)

TABLE XII Oil Filitration Data - Lightly Abused Cooking Oil (Compositegel) % Free Fatty Sample % T Acid Control (oil 70.2 2.34 alone) Inv. Ex.69.2 2.03 XXI(2% usage) Inv. Ex. XXI n/a 0.32 (6% usage) Inv. Ex. XX75.8 0.33 (6% usage)

Thus, the inventive gels exhibit utility comparable to commerciallyavailable cooking oil filtration products. It is expected that suchnovel gels will exhibit excellent properties in other areas as well.

While the invention will be described and disclosed in connection withcertain preferred embodiments and practices, it is in no way intended tolimit the invention to those specific embodiments, rather it is intendedto cover equivalent structures structural equivalents and allalternative embodiments and modifications as may be defined by the scopeof the appended claims and equivalence thereto.

1. A caustic composite silica gel exhibiting a pore volume of at least 1.00 cc/g and a surface area of at least 350 m²/g.
 2. The caustic composite silica gel of claim 1 wherein said gel includes at least one alkaline earth metal species thereon.
 3. The gel of claim 2 wherein said at least one alkaline earth metal species is selected from the group consisting of calcium, magnesium, or both.
 4. An oil filtration medium comprising at least one caustic composite silica gel as defined in claim
 1. 5. An oil filtration medium comprising at least one caustic composite silica gel as defined in claim
 2. 6. An oil filtration medium comprising at least one caustic composite silica gel as defined in claim
 3. 7. A method of producing a caustic composite silica gel material comprising the sequential process steps of a) initially producing a silicic acid sol through alkali metal silicate addition to a mineral acid, wherein the reaction occurs at a target pH level of between 1.5 and 4.0; b) quenching said silicic acid sol in a hot water medium to solidify said sol into a polysilicic acid gel, optionally in the presence of a water-insoluble pH adjusting material that imparts an increase in pH; c) aging the resultant gel of step “b” in salt water, optionally in the presence of a water-insoluble pH adjusting material that imparts an increase in pH; d) washing said aged gel of step “c” to remove excess salt; and e) drying said washed gel of step “d” to form a dry caustic silica gel; wherein at least of the optional presence of a water-insoluble pH adjusting material is included within either or both of steps “b” and “c”.
 8. The method of claim 7 wherein said water-insoluble pH adjusting material is selected from the group consisting of alkaline earth metal hydroxides.
 9. The method of claim 8 wherein said alkaline earth metal hydroxides are either calcium hydroxide or magnesium hydroxide. 